To protect the fireproof lining of a furnace from excessive thermal stress, cooling is frequently provided for the wall of the furnace. In the case of electric arc furnaces, so-called cooling panels are incorporated in the furnace wall. Liquid coolant flows through the cooling panels, frequently in the form of water.
DE 30 48 025 A1 describes a cooling device of this kind for an electric arc furnace. The cooling devices are arranged in contact with the furnace chamber. As a result, they are themselves exposed to high mechanical and thermal stresses. For example, the area of the cooling device is repeatedly subject to cracking or leakages resulting in the ingress of liquid coolant into the hot furnace chamber. A coolant ingress of this kind into the hot furnace chamber is hazardous since the coolant evaporates abruptly. Depending upon the size of the leakage, an actual explosion may occur which can cause serious damage to the furnace and also endanger the life of the furnace operator.
It has been found that leakages in cooling devices are initially generally small and relatively little coolant enters the furnace chamber. However, due to the high mechanical and thermal stress on the cooling device, the fine cracks that form and through which the coolant can escape, rapidly enlarge.
Therefore, the earlier a leakage in the area of the cooling device of a furnace is detected, the sooner it is possible to counteract an impending explosion and prevent damage to the furnace and risk to the life and body of the operator. Existing systems for the early detection of leakages in cooling devices of furnaces do not meet the requirements relevant to safety issues since the accuracy and unambiguousness of existing measuring methods is not sufficient.
For example, attempts have already been made to obtain information on leakages by taking differential measurements of coolant pressure on different cooling devices of a furnace. A leakage results in loss of coolant in a cooling device and hence to a loss of pressure in the cooling device affected. However, due to the generally high quantities of coolant in each cooling device and the usually widely branched supply and discharge system, this method has been found to be too slow and imprecise for the detection of leakages.
When water is used as a coolant, which is frequently the case, there are also already measuring systems in use which detect the hydrogen content in the stream of exhaust gas of the furnace and use this value to determine the amount of water contained in the exhaust gas by inverse calculation. Since water entering the furnace chamber does not always decompose into hydrogen and oxygen, but water vapor can be contained in the stream of exhaust gas, and in addition combustion processes normally take place which entail the formation of carbon dioxide and water and wherein the water dissociates with the formation of hydrogen, once again, this method is not informative enough for reliable detection of leakages.
U.S. Pat. No. 7,223,978 B2 describes a general method for determining the amount of chemical components in a hot gas, in particular in an electric arc furnace, wherein the determination of the carbon dioxide, carbon monoxide, oxygen or water content is performed by means of a laser diode.